1. Field of the Invention
The present invention generally relates to the marking of the body of an object with a permanent indicium or mark. More specifically, the invention relates to using a high energy density beam, such as a laser light, to permanently mark a plastic product in a subsurface location after fully forming, or substantially fully forming, the product.
2. Related Technology
In many industries, it is desirable to mark a product to limit counterfeiting, facilitate tracking, or aid in performance verification and/or traceability for regulatory compliance.
One technology in which marking occurs for regulatory compliance purposes is automotive safety glazings, such as windshields, side windows and backlites (rear windows). The requirements for such marks are set out in Section 7 of ANSI/SAE Z26.1-1996 and in Paragraph S6.2 of 49CFR571.205. These requirements relate to both the form of the mark and the performance that it certifies. With regard to form, the regulations set forth requirements with regard to legibility, minimum height of letters and numerals and permanence of the mark. Regarding performance, the above regulations require that the glazing manufacturer certify, by adding the appropriate mark, that the glazing meets certain requirements regarding optical transmissivity, impact resistance, abrasion resistance and the like. The implication of this requirement is that the achievement of these performance standards should precede the actual marking of the glazing. From a manufacturing standpoint, this means that, in all aspects that bear on performance, the glazing product should be fully formed, or substantially fully formed, prior to certification by marking.
Today's automotive vehicles typically utilize glazings that are made of glass. In order to effectuate the marking of glass glazings, various methods have been used. The two most widely used methods are physical etching and chemical etching. With physical etching, the part is sandblasted to physically form the mark in the product. With chemical etching, various chemicals are used to dissolve portions of the glazing so as to form the mark. More recently, glass glazings have been marked using high energy density beams, such as laser lights.
Also recently, automotive glazings have been manufactured from materials other than glass. Specifically, plastic materials, such as polycarbonate, have been used to replace glass in various automotive glazing applications including side windows, backlites and moon roofs. While plastic materials give more freedom in the style and shape of the glazing, plastic glazings offer challenges beyond those found in glass glazings. For example, plastic glazings are susceptible to degradation when exposed to ultraviolet radiation, such as that found in sunlight. Additionally, the plastics used in these glazings are softer than glass and, therefore, more susceptible to abrasion by external elements.
To overcome these and other limitations, plastic glazing systems have been developed with a plastic substrate coated with at least one protective coating. Typically, at least two protective coatings are employed, namely a weathering coating and an abrasion resistant coating. The weathering coating specifically reduces the amount of ultraviolet radiation penetrating to the underlying plastic substrate. The abrasion resistant coating, located exteriorly at the weathering coating, resists abrasion that results from exposure to external elements such as dirt, sand and other road debris.
As noted above, the governmental regulations for glazings requires the glazing manufacturer to certify that each piece of glazing meets various requirements (e.g., to ensure a necessary degree of transparency and abrasion resistance in the glazing for driver visibility). This certification requires the addition of ‘DOT’ and a manufacturer code (assigned by the National Highway and Transportation Safety Administration to the manufacturer of the glazing) to the glazing. The certification requirement implies that the glazing meets the applicable performance standards prior to receiving the mark. Thus, when viewed from a manufacturing standpoint, the regulations implicitly require that, before marking occurs, the glazing be fully formed in all aspects that bear on certification. Protective coatings applied over the plastic substrate generally impact the abrasion resistance and the optical transmissivity of the glazing and, therefore, in the spirit of the regulation, the panels should not be marked until after the protective coatings have been applied.
Applying a mark to the plastic glazing after the application of the protective coatings, however, presents several issues. First, application of the mark itself must not adversely affect the protective coatings or the underlying substrate. Additionally, application of the mark must comply with the permanence requirements and not be subject to wear and obliteration, resulting from the rubbing and scraping of the mark. While the spirit of the regulation requires the application of the mark after the plastic glazing has been fully, or substantially fully, manufactured, if a feature were to be applied directly to the plastic substrate before the application of a wet coat protective coating, a resulting visibility defect, typically an optical distortion around the mark, may result around that feature.